It is possible that people with asthma are more likely to be affected by altitude sickness.
However, fit, healthy people with well-controlled asthma should have no problems coping with high altitudes provided that they ascend slowly and recognise and accept their limitations, adjusting their medicine if need be.
In freezing conditions, pressurised inhalers may not work properly. They should be warmed (e.g. in the hands) before use.
In addition, the conditions are high altitudes are often dry and cold, and these conditions tend to exacerbate and trigger asthma. People whose asthma is triggered by cold conditions might find that high altitudes are a problem, as the air temperature usually decreases at higher altitudes.
Also, climbing can be a very strenuous exercise and this may trigger exercise-induced asthma in some people. However, people whose asthma is triggered by house-dust mites may find that their asthma improves, as the house-dust mite cannot survive at altitudes higher than ‘the snow line’.
People with asthma who fly directly into a place that is at high altitude will not have time to acclimatise and may experience problems. This should be discussed with a doctor so that the altitude reached by aircraft should not pose problems for people with asthma.
The best thing to do is to discuss your trip with your doctor several weeks in advance of your departure. This will allow time to work out a personal asthma action plan for the trip. This might involve increasing your preventer treatment for several weeks before the trip to give the airways extra protection, or measuring peak flow while away to determine how altitude is affecting your lung function, or even simple things like ensuring that you have enough medication and backup medication.